1. Field of the Invention
The present invention deals with some important improvements in the functional attachment system for osteosynthesis, preferably applicable to the osteosynthetic technique for external devices. The known techniques are the subject of Spanish Pat. No. 483.191 by the same inventor.
2. Description of the Prior Art
The system described in the aforementioned Spanish Pat. No. 483.191 is based on the mechanical or biomechanical principle consisting of the utilization of some sliding devices parallel to the damaged or fractured bone in such a way that the muscular contraction is converted into an impact or compression at the fracture focus between the fragments equal in magnitude and opposite to said contraction. A similar effect is produced by the action of muscle "tone," which is a state of minor permanent contraction, or by the action of gravity and load.
The principle is carried out whenever in external osteosynthesis use is made of mechanical devices that neutralize or tend to neutralize all angular, lateral or rotational movements, with movement in the direction of the longitudinal or major axis of the bone remaining free.
Hence this is osteosynthesis in which the "bridge," with a solid osseous anchor, is formed of one or more parts sliding together.
All current osteosynthetic systems are based on achieving absolute rest for the focus, and include those systems which maintain compression at the focus by means of endless screw systems, in order to increase stability; but in all these techniques, the compression is virtually invariable and its magnitude entirely empirical.
In the system under the Spanish Pat. No. 483.191 mentioned above, the magnitude of the compression is variable in relation to the function which, from least to greatest importance are muscular tone (rest); muscular contraction (movement); weight (bipedal standing); and dynamic load (walking; weight multiplied by acceleration).
External fasteners for the treatment of fractures, especially open and serious ones, comprise transfixion clips or studs which, by attaching to the two or more fragments of a fractured bone, unified externally relative to the bone by means of metal bars. These bars and the transfixing clips or studs are held together by holding means such as clamps or articulated joints ball-and-socket joints.
There are on the world market more than 50 models of external fasteners of various mechanical form but essentially having the same principles. In all of them, the joining bars are of two types.
1. Neutralizing bars. These are simple metal bars, generally steel, in several sections, for the most part cylindrical and of various diameters and lengths.
2. Compression bars. These are formed of endless-screw devices, blockable, that make it possible to apply compression by prestressing same and the entire system. When the endless screw is blocked, the pressure applied is theoretically maintained constant.
These are models in which the pressure is exerted not by a screw but by rubber bands or springs.
The functional attachment system for osteosynthesis constituting the reason and basis for Spanish Pat. No. 483.191 is based on giving the bars a telescopic arrangement, sliding together according to the simplest prototype formed by a double tube in which the exterior is greater in diameter and with an internal diameter equal to the outside of the interior.
When each of these telescopic parts is made solid with the two fragments of a fracture by means of appropriate clamps or ball-and-socket joints and this bar is placed parallel to the major axis of the bone, an axial compression is produced in the area of the fracture by the action of the muscles. It should be pointed out here that the muscle is never completely relaxed, but rather even in this state maintains a degree of permanent contraction called muscle "tone." That is, the fracture remains subjected to a permanent compression by this muscle "tone," but variable at all times in relation to position and function.
Said telescopic sliding bars, while maintaining longitudinal movement, cancel out angular, rotational and other movements that are harmful to the healing of the fracture.
By means of the functional attachment system set forth in the aforementioned Spanish patent, it is possible to utilize mechanical compression stimuli on the focus that are of physiologically varying magnitude corresponding to muscular tone, muscual contraction, static load and dynamic load.
In general terms, most of the presently existing fastener systems for osteosynthesis consist of a number of elements or parts with which each total assembly is constructed; these elements or parts may be quite varied, as for example single, double, double in a square, in a triangle, in double square or irregular, these terms corresponding to the number of bars used and the location of same in space. The diversity of types and locations of fractures makes it possible to use in each case the most appropriate assembly in relation to the type of fracture and the mechanical needs of each situation.